1. Field of the Invention
The present invention relates to an apparatus for cutting coupons from a plastic web material to form bag handle apertures.
2. Prior Art
It is known to form bags from tubular feed stock of thermoplastic web material wherein the tubular stock is flattened such that the side edge creases or gussets are formed which define the bottom of the bag. The web material is fed into a bag machine where it is generally cut longitudinally to form the bag handles. The bag machine subsequently cuts and seals the plastic web transversely in the direction of tube elongation to form the sides of the bag. During the manufacture of the bag, it is known to cut circular apertures from the web material to form the bag handles.
A problem associated with these bag machines is that the web material is a flexible stock which tends to cause it to flow or move in directions other than the direction it is being drawn into the bag machine. This makes it difficult to cut the bag handle apertures accurately. Further, the thinner the material used for the plastic web the more the material has a tendency to float.
As can be appreciated, it is important that the handle aperture cut into the bag be an even cut since any jagged edges or tears in the bag handle aperture are weak points which cause premature bag failure under loaded conditions.
Presently, it is common to heat the circular blade to improve the cut of the bag handle aperture. The blade is heated to allow the blade to cut through the plastic web material easier. This increases the blade wear life resulting in less down time for the bag making machine to replace blades.
In the art the term "heat window" is used to define a function of the difference between the heat required to provide an effective cut and the heat at which the plastic web adheres to the blade. With improvements in the plastic art the "heat window" has diminished to the point that it is not practical to obtain a continuous effective cut. These improvements in the plastic art have also brought cheaper, stronger and thinner plastic webs. And, apart from the "heat window" difficulties they are difficult to cut by conventional cutting methods.
The use of heat facilitates cutting and in the absence of heat the accuracy of the blade setting is very demanding. If the blade and cutting surface are not properly aligned the coupon cut is frequently ragged or incomplete.
The maintenance of cut is particularly difficult in high-speed application and where the blade is not correctly set leads to uneven wear with the necessity of frequent maintenance and replacement.
It is therefore an object of the present invention to provide an improved apparatus for cutting coupons from plastic webs which obviates the use of heated cutting blades and will cut coupons from the thinner gauge plastic webs of the present state of the plastic art.
It is another object of the present invention to provide a coupon-cutting mechanism which will permit a uniform cut and accommodate variations in the blade and surface settings to provide a more consistent cut and reduced wear on the blades.